Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.57	4.264%	$18.3192	$18.32	$18.30	$18.30
Purchase #2	$182.44	9.667%	$200.0765	$200.08	$200.10	$200.10
Purchase #3	$5.38	13.341%	$6.0977	$6.10	$6.10	$6.10
Purchase #4	$250.54	8.308%	$271.3549	$271.35	$271.35	$271.40
Purchase #5	$39.54	8.794%	$43.0171	$43.02	$43.00	$43.00
Purchase #6	$144.64	5.440%	$152.5084	$152.51	$152.50	$152.50
Purchase #7	$143.77	11.573%	$160.4085	$160.41	$160.40	$160.40
7 purchase totals =	$783.88		$851.7823	$851.79	$851.75	$851.80